KR102610616B1 - Non-aqueous electrolyte, semi-solid electrolyte layer, secondary battery sheet and secondary battery - Google Patents

Abstract

The object is to provide a non-aqueous electrolyte that can improve the input/output characteristics of a secondary battery, and especially the lifespan and rate characteristics at high temperatures. The non-aqueous electrolyte solution of the present invention includes a solvated ionic liquid having sulfolane and/or a derivative thereof and an electrolyte salt, an optional low-viscosity organic solvent, and an optional negative electrode interface stabilizer, at room temperature of the low-viscosity organic solvent. The equilibrium vapor pressure of is 1 Pa or more, the ratio of the number of moles of the solvated ionic liquid to the total number of moles of the solvated ionic liquid and the low-viscosity organic solvent is X, and the solvated ionic liquid and the low-viscosity organic solvent When the ratio of the weight of the negative electrode interface stabilizer to the total weight is Y (%), it satisfies Y≤142.86X-11.429.

Description

Non-aqueous electrolyte, semi-solid electrolyte layer, secondary battery sheet and secondary battery

The present invention relates to a non-aqueous electrolyte solution, a semi-solid electrolyte layer, a sheet for a secondary battery, and a secondary battery.

As a prior art regarding non-aqueous electrolyte solutions used in various secondary batteries, Patent Document 1 discloses a non-aqueous electrolyte solution for secondary batteries containing an electrolyte, a non-aqueous solvent, and a predetermined compound having a carbon atom bonded to three oxygen atoms in the molecule. there is. The non-aqueous solvent may contain a sulfone-based compound such as sulfolane, and the amount of the sulfone-based compound is preferably 0.3 volume% or more, more preferably 1 volume% or more, based on 100 volume% of the non-aqueous solvent. It is preferably 5 volume% or more, more preferably 40 volume% or less, more preferably 35 volume% or less, and even more preferably 30 volume% or less.

Japanese Patent Publication No. 2018-029034

Patent Document 1 does not describe or suggest the use of sulfolane as a component of a solvated ionic liquid or the change in input/output characteristics of a secondary battery depending on the sulfolane content in that case. Therefore, there is a possibility that sufficient input/output characteristics of the secondary battery cannot be obtained with the technology of Patent Document 1. In particular, when sulfolane is simply contained in the non-aqueous electrolyte, there is a risk that the lifespan of the secondary battery at high temperatures may be reduced or sufficient rate characteristics may not be obtained, but Patent Document 1 does not examine this problem.

Therefore, the purpose of the present invention is to provide a non-aqueous electrolyte that can improve the input/output characteristics of a secondary battery, and especially the lifespan and rate characteristics at high temperatures. Another object is to provide a semi-solid electrolyte layer, a sheet for a secondary battery, and a secondary battery using the non-aqueous electrolyte solution.

The present inventors, in a non-aqueous electrolyte solution containing a solvated ionic liquid containing sulfolane and/or its derivative and an electrolyte salt, an optional low-viscosity organic solvent, and an optional negative electrode interface stabilizer, the mixing ratio of each component is set to a predetermined amount. It was found that the above problem was solved by adjusting within the range, and the invention was completed.

That is, the non-aqueous electrolyte solution of the present invention includes a solvated ionic liquid having sulfolane and/or its derivative and an electrolyte salt, an optional low-viscosity organic solvent, and an optional negative electrode interface stabilizer, and the low-viscosity organic solvent The equilibrium vapor pressure at room temperature is 1 Pa or more, the ratio of the number of moles of the solvated ionic liquid to the total number of moles of the solvated ionic liquid and the low-viscosity organic solvent is X, and the solvated ionic liquid and the low-viscosity organic solvent are When the ratio of the weight of the negative electrode interface stabilizer to the total weight of the organic solvent is Y (%),

Y≤142.86X-11.429

It is characterized by satisfying .

This specification includes the disclosure of Japanese Patent Application No. 2019-039934, which is the basis of priority herein.

The input/output characteristics of a secondary battery can be improved by the non-aqueous electrolyte of the present invention. Additionally, the lifespan of the secondary battery at high temperatures can be increased and the rate characteristics can be improved. Problems, configurations, and effects other than those described above will be revealed by the description of the embodiments below.

1 is a cross-sectional view of a lithium ion secondary battery according to this embodiment.
Figure 2 is a graph showing the relationship between the molar ratio X and the weight ratio Y (%) in examples and comparative examples.
Figure 3 is a graph showing the change in discharge capacity maintenance rate at 40°C with respect to molar ratio X in Examples and Comparative Examples.

Hereinafter, embodiments of the present invention will be described using drawings and the like. The following description shows specific examples of the content of the present invention, but the present invention is not limited to these descriptions, and various changes and modifications can be made by those skilled in the art within the scope of the technical idea disclosed in this specification. In addition, in all drawings for explaining the present invention, parts having the same function are given the same reference numerals, and repeated descriptions thereof may be omitted.

“To” described in this specification is used to mean that the numerical values described before and after are used as the lower limit and the upper limit. In the numerical range described in steps in this specification, the upper limit or lower limit described in one numerical range may be replaced by the upper or lower limit value described in other steps. The upper or lower limit of the numerical range described in this specification may be replaced with the value shown in the examples.

An embodiment of the secondary battery according to the present invention will be described below by taking a lithium ion secondary battery as an example. A lithium ion secondary battery is an electrochemical device that stores or makes available electrical energy by inserting and releasing lithium ions from an electrode in an electrolyte. Lithium ion secondary batteries are also called by other names such as lithium ion batteries, non-aqueous electrolyte secondary batteries, and non-aqueous electrolyte secondary batteries, and any battery is the subject of the present invention. The technical idea of the present invention can also be applied to sodium ion secondary batteries, magnesium ion secondary batteries, calcium ion secondary batteries, zinc secondary batteries, aluminum ion secondary batteries, etc.

When selecting a material from the group of materials exemplified below, materials may be selected individually or in combination, as long as they do not contradict the content disclosed in this specification. Within the range that does not conflict with the above, materials other than the material group exemplified below may be selected.

1 is a cross-sectional view of a lithium ion secondary battery according to an embodiment of the present invention. Figure 1 shows a stacked lithium ion secondary battery, and the lithium ion secondary battery 1000 has a positive electrode 100, a negative electrode 200, an exterior body 500, and an insulating layer 300. The exterior body 500 accommodates the insulating layer 300, the positive electrode 100, and the negative electrode 200. The exterior body 500 is selected from a group of materials that are corrosion resistant to non-aqueous electrolyte solutions, such as aluminum, stainless steel, and nickel-plated steel. The lithium ion secondary battery can also have a wound type configuration.

In the lithium ion secondary battery 1000, an electrode body 400 composed of a positive electrode 100, an insulating layer 300, and a negative electrode 200 is stacked to form an electrode group. Hereinafter, the positive electrode 100 or the negative electrode 200 may be referred to as an electrode. Additionally, a stack of the positive electrode 100 or the negative electrode 200, or both, and the insulating layer 300 may be referred to as a secondary battery sheet. When the insulating layer 300 and the electrode have an integrated structure, an electrode group can be manufactured simply by stacking secondary battery sheets.

The positive electrode 100 has a positive electrode current collector 120 and a positive electrode mixture layer 110. A positive electrode mixture layer 110 is formed on both sides of the positive electrode current collector 120. The negative electrode 200 has a negative electrode current collector 220 and a negative electrode mixture layer 210. A negative electrode mixture layer 210 is formed on both sides of the negative electrode current collector 220. The positive electrode mixture layer 110 or the negative electrode mixture layer 210 may be referred to as an electrode mixture layer, and the positive electrode current collector 120 or negative electrode current collector 220 may be referred to as an electrode current collector.

The positive electrode current collector 120 has a positive electrode tab 130. The negative electrode current collector 220 has a negative electrode tab 230. The positive electrode tab 130 or the negative electrode tab 230 may be referred to as an electrode tab. No electrode mixture layer is formed on the electrode tab. However, an electrode mixture layer may be formed on the electrode tab as long as it does not adversely affect the performance of the lithium ion secondary battery 1000. The positive electrode tab 130 and the negative electrode tab 230 protrude to the outside of the exterior body 500, and the plurality of protruding positive electrode tabs 130 and the plurality of negative electrode tabs 230 are bonded, for example, by ultrasonic bonding. By joining, etc., a parallel connection is formed within the lithium ion secondary battery 1000. The lithium ion secondary battery according to the present invention can also be configured as a bipolar type with electrical series connections within the secondary battery.

The positive electrode mixture layer 110 includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The negative electrode mixture layer 210 includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. The positive electrode active material or negative electrode active material may be referred to as an electrode active material, the positive electrode conductive agent or negative electrode conductive agent may be referred to as an electrode conductive agent, and the positive electrode binder or negative electrode binder may be referred to as an electrode binder.

<Electrode challenge>

The electrode conductive agent improves the conductivity of the electrode mixture layer. As an electrode conductive agent, it can be appropriately selected and used from the group of materials such as Ketjen black, acetylene black, and graphite.

<Electrode binder>

The electrode binder binds the electrode active material, electrode conductive agent, etc. in the electrode. As the electrode binder, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyvinylidene fluoride (PVDF), copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (P(VdF- It can be used by appropriately selecting from the group of materials such as HFP)).

<Positive electrode active material>

In the positive electrode active material showing a noble potential, lithium ions are desorbed during the charging process, and lithium ions desorbed from the negative electrode active material are inserted during the discharging process. As a positive electrode active material, a lithium composite oxide containing a transition metal is preferable. Specifically, LiMO ₂ , Li[LiM]O ₂ with a Li excess composition, LiM ₂ O ₄ , LiMPO ₄ , LiMVO ₄ , LiMBO ₃ , Li ₂ MSiO ₄ (where M is Co, Ni, Mn, Fe, and at least one selected from Cr, Zn, Ta, Al, Mg, Cu, Cd, Mo, Nb, W, Ru, etc.). Additionally, part of the oxygen in these materials may be replaced with other elements such as fluorine. In addition, the positive electrode active material includes chalcogenides such as TiS ₂ , MoS ₂ , Mo ₆ S ₈ , and TiSe ₂ , vanadium-based oxides such as V ₂ O ₅ , halides such as FeF _{3 ,} and Fe(MoO _{4 )} that constitutes a polyvalent anion. ) ₃ , Fe ₂ (SO ₄ ) ₃ , Li ₃ Fe ₂ (PO ₄ ) ₃ , quinone-based organic crystals, oxygen, etc., and may include at least one selected from the group of materials.

<Positive electrode current collector (120)>

As the positive electrode current collector 120, aluminum foil with a thickness of 1 to 100 μm, aluminum perforated foil with holes with a thickness of 10 to 100 μm and a hole diameter of 0.1 to 10 mm, expanded metal, foamed metal plate, stainless steel, It can be used by appropriately selecting from a group of materials such as titanium.

<Negative active material>

In the negative electrode active material showing a low potential, lithium ions are desorbed during the discharging process, and lithium ions desorbed from the positive electrode active material in the positive electrode mixture layer 110 are inserted during the charging process. As negative electrode active materials, carbon-based materials (graphite, graphitized carbon materials, amorphous carbon materials, organic crystals, activated carbon, etc.), conductive polymer materials (polyacene, polyparaphenylene, polyaniline, polyacetylene, etc.), lithium complex oxide (titanium) Lithium acid: Li ₄ Ti ₅ O ₁₂ or Li ₂ TiO ₄ , etc.), metal lithium, metal alloyed with lithium (having at least one type of aluminum, silicon, tin, etc.), or their oxides. there is.

<Negative electrode current collector (220)>

As the negative electrode current collector 220, copper foil with a thickness of 1 to 100 μm, perforated copper foil with a thickness of 1 to 100 μm and a hole diameter of 0.1 to 10 mm, expanded metal, foamed metal plate, stainless steel, titanium, and nickel. It can be used by appropriately selecting from the group of materials such as:

<Electrode>

An electrode mixture layer is produced by attaching an electrode slurry containing an electrode active material, an electrode conductive agent, an electrode binder, and a solvent to an electrode current collector using a coating method such as a doctor blade method, dipping method, or spray method. The solvent is selected from the group of materials such as N-methylpyrrolidone (NMP) and water. Afterwards, the electrode mixture layer is dried to remove the solvent, and the electrode mixture layer is pressure-molded using a roll press to produce an electrode.

When the electrode mixture layer contains a non-aqueous electrolyte solution, the content of the non-aqueous electrolyte solution in the electrode mixture layer is preferably 20 to 40% by volume. If the content of the non-aqueous electrolyte solution is small, the ion conduction path inside the electrode mixture layer may not be sufficiently formed, and the rate characteristics may deteriorate. Moreover, when the content of the non-aqueous electrolyte solution is high, in addition to the possibility that the non-aqueous electrolyte solution leaks from the electrode mixture layer, the relative amount of the electrode active material becomes insufficient, which may lead to a decrease in energy density.

In order to contain the non-aqueous electrolyte solution in the electrode mixture layer, the non-aqueous electrolyte solution is injected into the lithium ion secondary battery 1000 from one open side or injection hole of the exterior body 500, and the pores of the electrode mixture layer are filled with the non-aqueous electrolyte solution. You can. Alternatively, a slurry containing a mixture of a non-aqueous electrolyte solution, an electrode active material, an electrode conductive agent, and an electrode binder may be prepared, and the prepared slurry may be applied together on an electrode current collector to fill the pores of the electrode mixture layer with the non-aqueous electrolyte solution. As a result, the particles of the electrode active material or electrode conductive agent in the electrode mixture layer function as supporting particles without the need for supporting particles contained in the semi-solid electrolyte, and the non-aqueous electrolyte solution can be maintained by these particles.

The thickness of the electrode mixture layer is preferably equal to or greater than the average particle diameter of the electrode active material. If the thickness of the electrode mixture layer is small, electronic conductivity between adjacent electrode active materials may deteriorate. If there are coarse particles in the electrode active material powder with an average particle diameter greater than the thickness of the electrode mixture layer, it is preferable to remove the coarse grains in advance by sieve classification, wind classification, etc. to obtain particles less than the thickness of the electrode mixture layer.

<Insulating layer (300)>

The insulating layer 300 serves as a medium for transferring ions between the positive electrode 100 and the negative electrode 200. The insulating layer 300 also acts as an electronic insulator and prevents short circuit between the positive electrode 100 and the negative electrode 200. The insulating layer 300 has a semi-solid electrolyte layer. As the insulating layer 300, a separator and a semi-solid electrolyte layer may be used together.

<Separator>

A porous sheet can be used as a separator. The porous sheet is made of cellulose, modified forms of cellulose (carboxymethylcellulose (CMC), hydroxypropylcellulose (HPC), etc.), polyolefin (polypropylene (PP), propylene copolymer, etc.), polyester (polyethylene terephthalate ( PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), etc.), polyacrylonitrile (PAN), polyaramid, polyamidoimide, polyimide, resin, and glass. there is. By making the separator larger than the positive electrode 100 or the negative electrode 200, short circuit between the positive electrode 100 and the negative electrode 200 can be prevented.

A separator may be formed by applying a separator forming mixture containing separator particles, a separator binder, and a solvent to the electrode mixture layer. Alternatively, the separator forming mixture may be applied to the porous sheet.

The separator particles are selected from the group of materials such as γ-alumina (Al ₂ O ₃ ), silica (SiO ₂ ), and zirconia (ZrO ₂ ). The average particle diameter of the separator particles is preferably 1/100 to 1/2 of the thickness of the separator. The separator binder can be selected from the group of materials such as polyethylene (PE), PP, polytetrafluoroethylene (PTFE), PVDF, P(VdF-HFP), styrene butadiene rubber (SBR), polyalginic acid, and polyacrylic acid.

When the insulating layer 300 includes a separator, the separator can be filled with the non-aqueous electrolyte by injecting the non-aqueous electrolyte into the lithium ion secondary battery 1000 from one open side of the exterior body 500 or the injection hole.

<Semi-solid electrolyte layer>

The semi-solid electrolyte layer has a semi-solid electrolyte binder and a semi-solid electrolyte. A semi-solid electrolyte has supported particles and a non-aqueous electrolyte solution. The semi-solid electrolyte has pores formed by an aggregate of supported particles, in which a non-aqueous electrolyte solution is held. By maintaining the non-aqueous electrolyte in the semi-solid electrolyte, the semi-solid electrolyte allows lithium ions to pass through. When the electrode mixture layer is filled with a non-aqueous electrolyte using a semi-solid electrolyte layer as the insulating layer 300, injection of the non-aqueous electrolyte into the lithium ion secondary battery 1000 becomes unnecessary. In cases where the insulating layer 300 has a separator, etc., the non-aqueous electrolyte may be injected into the lithium ion secondary battery 1000 from one open side of the exterior body 500 or a liquid injection hole.

The semi-solid electrolyte layer contains a liquid component such as a non-aqueous electrolyte and can be handled like a solid, and may be a translucent self-supporting membrane. Locally, liquid components such as non-aqueous electrolytes are responsible for lithium ion conduction, showing high ionic conductivity. In other words, the semi-solid electrolyte layer combines the advantages of both the high safety of a solid and the high ionic conductivity of a liquid.

Methods for producing a semi-solid electrolyte layer include a method of compression molding a semi-solid electrolyte powder into a pellet shape using a molding die or a method of adding and mixing a semi-solid electrolyte binder to the semi-solid electrolyte powder to form a sheet. By adding and mixing a semi-solid electrolyte binder with semi-solid electrolyte powder, a highly flexible sheet-like semi-solid electrolyte layer can be produced. A semi-solid electrolyte layer may be produced by adding and mixing a solution of a binder obtained by dissolving a semi-solid electrolyte binder in a dispersion solvent into the semi-solid electrolyte, applying the mixture on a base material such as an electrode, and distilling off the dispersion solvent by drying.

<Supporting particles>

The supporting particles are preferably insulating particles and insoluble in non-aqueous electrolyte solution from the viewpoint of electrochemical stability. The supported particles are selected from the group of materials such as oxide inorganic particles such as SiO ₂ particles, Al ₂ O ₃ particles, ceria (CeO ₂ ) particles, and ZrO ₂ particles, and solid electrolytes. By using oxide inorganic particles as supporting particles, the non-aqueous electrolyte solution can be maintained at a high concentration within the semi-solid electrolyte layer. Additionally, since no gas is generated from the oxide inorganic particles, a semi-solid electrolyte layer can be produced by a roll-to-roll process in air. The solid electrolyte is appropriately selected from the group of materials such as oxide-based solid electrolytes such as Li-La-Zr-O and sulfide-based solid electrolytes such as Li ₁₀ Ge ₂ PS ₁₂ .

Since the retention amount of the non-aqueous electrolyte solution is considered to be proportional to the specific surface area of the supported particles, the average particle diameter of the primary particles of the supported particles is preferably 1 nm to 10 ㎛. If the average particle diameter of the primary particles of the supporting particles is large, the supporting particles may not be able to properly maintain a sufficient amount of non-aqueous electrolyte solution, making it difficult to form a semi-solid electrolyte. In addition, if the average particle diameter of the primary particles of the supporting particles is small, the surface interfacial force between the supporting particles increases, making it easy for the supporting particles to agglomerate, which may make it difficult to form a semi-solid electrolyte. The average particle diameter of the primary particles of the supported particles is more preferably in the range of 1 to 50 nm, and even more preferably in the range of 1 to 10 nm. The average particle diameter of the primary particles of the supported particles can be measured using TEM.

<Non-aqueous electrolyte>

A non-aqueous electrolyte solution has a non-aqueous solvent. Non-aqueous solvents include solvated ionic liquids, optional low-viscosity organic solvents, and optional negative interface stabilizers. In the following description, the solvated ionic liquid may be referred to as the main solvent. Components contained in the non-aqueous electrolyte can be measured by NMR or the like.

An ionic liquid is a compound that dissociates into cations and anions at room temperature and maintains a liquid state. Ionic liquids are sometimes called ionic liquids, low melting point molten salts, or room temperature molten salts. From the viewpoint of stability in the atmosphere and heat resistance in a secondary battery, the non-aqueous solvent is preferably low volatile and has a vapor pressure of 150 Pa or less at room temperature, but is not limited thereto. When the non-aqueous electrolyte solution contains a less volatile solvated ionic liquid, volatilization of the non-aqueous electrolyte solution from the semi-solid electrolyte layer can be suppressed.

The content of the non-aqueous electrolyte solution in the semi-solid electrolyte layer is not particularly limited, but is preferably 40 to 90% by volume. When the content of the non-aqueous electrolyte solution is small, the interfacial resistance between the electrode and the semi-solid electrolyte layer may increase. Additionally, if the content of the non-aqueous electrolyte solution is large, there is a risk that the non-aqueous electrolyte solution may leak from the semi-solid electrolyte layer. When the semi-solid electrolyte layer is in the form of a sheet, the content of the non-aqueous electrolyte solution in the semi-solid electrolyte layer is preferably 50 to 80 volume%, and further preferably 60 to 80 volume%. When forming a semi-solid electrolyte layer by applying a mixture of a semi-solid electrolyte and a solution obtained by dissolving a semi-solid electrolyte binder in a dispersion solvent onto an electrode, the content of the non-aqueous electrolyte solution in the semi-solid electrolyte layer is preferably 40 to 60% by volume.

The weight ratio of the main solvent in the non-aqueous electrolyte solution is not particularly limited, but from the viewpoint of the stability of the lithium ion secondary battery and to enable high-speed charging and discharging, the weight ratio of the main solvent in the non-aqueous electrolyte solution is 30 to 70. It is preferable that it is % by weight, especially 40 to 60% by weight, and further 45 to 55% by weight.

<Solvated ionic liquid>

The solvated ionic liquid contains sulfolane and/or its derivative and an electrolyte salt. When a solvated ionic liquid containing sulfolane and/or its derivative is used, the transport speed of lithium ions in the semi-solid electrolyte layer increases because sulfolane and/or its derivatives adopt a unique coordination structure between lithium ions. Therefore, unlike solvated ionic liquids with ether-based solvents and electrolyte salts, where the input/output characteristics of secondary batteries deteriorate as the viscosity increases, even if the viscosity of the solvated ionic liquids is increased, the input/output characteristics of secondary batteries with solvated ionic liquids decrease. The decline can be suppressed.

Derivatives of sulfolane include those in which the hydrogen atom bonded to the carbon atom constituting the sulfolane ring is substituted by a fluorine atom or an alkyl group. Specific examples include fluorosulfolane, difluorosulfolane, and methylsulfolane. Any one of these may be used individually, or a plurality may be used in combination.

The electrolyte salt is preferably one that can be uniformly dispersed in a low-viscosity organic solvent, and various lithium salts whose cations are lithium can be used. Examples include lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium tetra Fluoroborate (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium triflate, etc. can be mentioned. Any one type may be used individually, or multiple types may be used together.

Solvated ionic liquids containing sulfolane and/or its derivatives and electrolyte salts can be collectively expressed in terms of their apparent composition. For example, a solvated ionic liquid composed of sulfolane and _LiTFSI is expressed as Li(SL)

The mixing ratio of sulfolane and/or its derivative to the electrolyte salt is not particularly limited, but the molar ratio of (sulfolane and/or its derivative)/electrolyte salt is preferably within the range of 1.0 to 3.5.

<Low viscosity organic solvent>

Low-viscosity organic solvents lower the viscosity of the non-aqueous electrolyte and improve ionic conductivity. When the internal resistance of the non-aqueous electrolyte is large, the internal resistance of the non-aqueous electrolyte can be lowered by adding a low-viscosity organic solvent to increase the ionic conductivity of the non-aqueous electrolyte.

The equilibrium vapor pressure of the low-viscosity organic solvent at room temperature (25°C) is preferably 1 Pa or more. As a result, volatilization of low-viscosity organic solvents is suppressed, safety is improved, and the lifespan of the lithium ion secondary battery 1000 during high-temperature operation is improved. Equilibrium vapor pressure can be evaluated using a vapor pressure measuring device, etc.

It is preferable that the donor number of the low-viscosity organic solvent is 12 or more. As a result, the interaction between the low-viscosity organic solvent and lithium ions becomes stronger, making it difficult for the low-viscosity organic solvent to volatilize. The number of donors can be evaluated by NMR or the like.

Low-viscosity organic solvents with an equilibrium vapor pressure of 1 Pa or more and a donor number of 12 or more at room temperature (25°C) include propylene carbonate (PC), butylene carbonate (BC), ethylene carbonate (EC), and trimethyl phosphate. (TMP), triethyl phosphate (TEP), tris(2,2,2-trifluoroethyl) phosphite (TFP), γ-butyrolactone (GBL), dimethyl methylphosphonate (DMMP), etc. .

<Negative interface stabilizer>

When the non-aqueous electrolyte solution contains a negative electrode interface stabilizer, the rate characteristics of the secondary battery can be improved and the battery life can be improved. The negative electrode interface stabilizer can be appropriately selected from the group of materials such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

<Input/output characteristics>

The ratio of the number of moles of the solvated ionic liquid (A) to the total number of moles of the solvated ionic liquid (A) and the low-viscosity organic solvent (B) is calculated as When the ratio of the weight of the negative electrode interface stabilizer (C) to the total weight of the low-viscosity organic solvent (B) is Y(C/(A+B))(%),

Y≤142.86X-11.429

It is desirable to satisfy. The values of X and Y can be measured by NMR.

As the weight of the anode interface stabilizer increases, the transport speed of lithium ions increases and the coordination structure of sulfolane and/or its derivatives and lithium ions is disturbed, so there is a possibility that the input/output characteristics of the lithium ion secondary battery 1000 may be impaired. there is. Therefore, in order to improve the input/output characteristics of the lithium ion secondary battery 1000, it is preferable that the weight of the negative electrode interface stabilizer is small.

<Life characteristics>

Regarding the ratio More preferably, it is 0.39≤X≤0.93, and even more preferably, it is 0.45≤X≤0.87. By setting You can. In addition, by setting By suppressing a decrease in capacity, a decrease in the lifespan of the lithium ion secondary battery 1000 can be suppressed.

<Corrosion inhibitor>

The non-aqueous electrolyte may contain a corrosion inhibitor as needed. The corrosion inhibitor forms a film from which metal is difficult to elute even when the positive electrode current collector 120 is exposed to a high electrochemical potential. As a corrosion inhibitor, a material containing an anionic species such as PF ₆ or BF ₄ and also a cationic species having a strong chemical bond to form a stable compound in an atmosphere containing moisture is preferred.

One indicator that a compound is stable in the atmosphere is solubility in water and the presence or absence of hydrolysis. If the corrosion inhibitor is a solid, it is preferred that the solubility in water is less than 1%. Additionally, the presence or absence of hydrolysis can be evaluated by analyzing the molecular structure of the sample after mixing with water. Here, not being hydrolyzed means that the corrosion inhibitor absorbs moisture or mixes with water and then heats at 100°C or higher to remove moisture, and 95% of the residue shows the same molecular structure as the original corrosion inhibitor.

Corrosion inhibitors are expressed as (MR) ⁺ An ^- . The cation of (MR) ⁺ An ^- is (MR) ⁺ . M is selected from nitrogen (N), boron (B), phosphorus (P), or sulfur (S). R consists of a hydrocarbon group.

The anion of (MR) ⁺ An ^- is An ^- . As An ^- , BF ₄ ^- or PF ₆ ^- are suitably used. By setting the anion of the corrosion inhibitor to BF ₄ ^- or PF ₆ ^- , dissolution of the positive electrode current collector 120 can be effectively suppressed. This is thought to be because the F anion of BF ₄ ^- or PF ₆ ^- reacts with SUS or aluminum of the electrode current collector to form a passive film.

Corrosion inhibitors include quaternary ammonium salts such as tetrabutylammonium hexafluorophosphate (TBAPF ₆ ) and tetrabutylammonium tetrafluoroborate (TBABF ₄ ), and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI- BF ₄ ), 1-ethyl-3-methylimidazolium hexafluorophosphate (EMI-PF ₆ ), 1-butyl-3-methylimidazolium tetrafluoroborate (BMI-BF ₄ ), 1-butyl- It is selected from the group of imidazolium salt materials such as 3-methylimidazolium hexafluorophosphate (BMI-PF ₆ ). In particular, anions can appropriately suppress the dissolution of the PF ₆ ^-face positive electrode current collector 120.

The content of the corrosion inhibitor is preferably 0.5 to 20% by weight, more preferably 1 to 10% by weight, based on the total weight of the non-aqueous electrolyte solution. If the content of the corrosion inhibitor is small, the effect of suppressing dissolution of the electrode current collector may decrease, and battery capacity may decrease with charging and discharging. Additionally, if the content of the corrosion inhibitor is high, lithium ion conductivity decreases, and a lot of storage energy is consumed to decompose the corrosion inhibitor, which may result in a decrease in battery capacity.

<Semi-solid electrolyte binder>

As a semi-solid electrolyte binder, a fluorine-based resin is suitably used. The fluorine-based resin is selected from the group of materials such as PTFE, PVDF, and P(VdF-HFP). These materials may be used individually or in combination of multiple materials. By using PVDF or P(VdF-HFP), the adhesion between the insulating layer 300 and the electrode current collector is improved, thereby improving battery performance.

<Semi-solid electrolyte>

A semi-solid electrolyte is formed by supporting or holding the non-aqueous electrolyte solution on the supporting particles. As a method of producing a semi-solid electrolyte, a slurry of a semi-solid electrolyte is prepared by mixing a non-aqueous electrolyte and supporting particles at a specific volume ratio, adding and mixing an organic solvent such as methanol, and then spreading the slurry on a dishwasher or the like and distilling off the organic solvent to form a semi-solid. A method of obtaining electrolyte powder, etc. may be mentioned.

Example

Hereinafter, the present invention will be described in more detail through Examples and Comparative Examples, but the present invention is not limited to these Examples.

(Example 1)

(1) Production of lithium ion secondary battery

<Production of semi-solid electrolyte layer>

LiBF ₄ as an electrolyte salt, sulfolane (SL), and TBAPF ₆ as a corrosion inhibitor were each weighed and mixed to obtain a non-aqueous electrolyte solution. This non-aqueous electrolyte and fumed silica nanoparticles with a particle diameter of 7 nm were weighed and mixed at a volume ratio of 80:20 to obtain a powdery semi-solid electrolyte.

The semi-solid electrolyte powder and PTFE, a semi-solid electrolyte binder, were each weighed at a weight ratio of 95:5, placed in a mortar, and mixed evenly. This mixture was set in a hydraulic press through a PTFE sheet and pressed to a thickness of 200 μm to obtain an insulating layer 300 (semi-solid electrolyte layer). The mixing ratio of the liquid components included in the semi-solid electrolyte layer was evaluated by NMR, and the molar ratio of SL and LiBF ₄ was 2:1, and the solvated ionic liquid Li(SL) ₂ BF ₄ containing electrolyte salt and sulfolane was evaluated by NMR. The weight ratio of TBAPF ₆ was 2.5%. This semi-solid electrolyte layer was punched to a diameter of 16 mm.

<Positive electrode (100)>

Li(Ni, Co, Mn)O _2- based oxide as a positive electrode active material, acetylene black as a positive electrode conductive agent, and PVDF as a positive electrode binder dissolved in N-methylpyrrolidone were uniformly mixed at a predetermined ratio using a kneader. NMP was added to this mixture to obtain a slurry. The slurry was applied onto the Al foil as the positive electrode current collector 120 using a table-top coater and dried at 120°C to obtain the positive electrode 100. This positive electrode 100 was pressed at a predetermined pressure and cut into a diameter of 13 mm.

<Negative electrode (200)>

Graphite as the negative electrode active material and SBR and CMC as the negative electrode binder were uniformly mixed at a predetermined ratio using a kneader. Water was added to this mixture to obtain a slurry. The slurry was applied onto Cu foil, which is the negative electrode current collector 220, using a table-top coater and dried at 100°C to obtain the negative electrode 200. This negative electrode 200 was pressed at a predetermined pressure and cut into a diameter of 13 mm.

<Lithium ion secondary battery (1000)>

After sandwiching the semi-solid electrolyte layer with the positive electrode 100 and the negative electrode 200 and encapsulating it in a CR2032 type coin cell, the composition of the non-aqueous electrolyte in the final semi-solid electrolyte layer, the positive electrode 100, and the negative electrode 200 is shown in Table 1. A lithium ion secondary battery (1000) was manufactured by injecting a non-aqueous electrolyte into a CR2032 type coin cell.

(2) Characteristic evaluation of lithium ion secondary battery

<Evaluation method of output characteristics>

In the first cycle of charging, the lithium ion secondary battery 1000 was charged to 4.2V in constant current mode at 0.05C, and after the voltage reached 4.2V, it was maintained at a constant potential until the current value reached 0.005C. In the first cycle of discharge, the discharge capacity of the lithium ion secondary battery 1000 was measured by performing the discharge at 0.05 C in constant current mode until the voltage reached 2.7 V. Thereafter, the second cycle charging was performed in the same manner as the first cycle charging. In the second cycle of discharge, the discharge capacity of the lithium ion secondary battery 1000 was measured in constant current mode at 0.5 C until the voltage reached 2.7 V. The ratio of the capacity at 0.5C in the 2nd cycle to the discharge capacity at 0.05C in the 1st cycle is set as "Q_0.5/Q_0.05" and is shown in Table 1. All of the above measurements were performed at 25°C.

<Evaluation method of life characteristics>

The charging and discharging of the first cycle was performed similarly to the charging and discharging of the first cycle in the evaluation method of output characteristics. In the second cycle of charging, constant current charging was performed at 40°C from 0.3C to 4.2V, and then maintained at a constant potential until the current value reached 0.03C. In the second cycle of discharge, constant current discharge was performed at 0.3C until the voltage reached 2.7V. This was repeated 20 times, and the ratio of the discharge capacity at the 20th cycle to the discharge capacity at the 2nd cycle was taken as the discharge capacity maintenance rate (%). The measurement results are shown in Table 1.

(Examples 2 to 44 and Comparative Examples 1 to 6)

A lithium ion secondary battery was manufactured in the same manner as in Example 1 except that the composition of the non-aqueous electrolyte solution was adjusted as shown in Table 1, and the capacity ratio "Q_0.5/Q_0.05" and the discharge capacity maintenance rate (%) were measured. The measurement results are shown in Table 1.

(3) Results and Discussion

Figure 2 is a graph showing the relationship between the molar ratio X and the weight ratio Y (%) in examples and comparative examples. Additionally, Figure 3 is a graph showing the change in discharge capacity maintenance rate at 40°C with respect to the molar ratio X in Examples and Comparative Examples.

As shown in Table 1 and Figure 2, in all examples, that is, in the range satisfying Y≤142.86X-11.429, the capacity ratio "Q_0.5/Q_0.05" representing the input/output characteristics was 40% or more. On the other hand, Comparative Examples 1 to 6 all had capacity ratios below 40%. In addition, in all examples where the discharge capacity retention rate was measured, that is, in the range satisfying 0.35≤X<1, the discharge capacity retention rate showing the life characteristics was 75% or more. In particular, in examples satisfying 0.39≤X≤0.93, it was more than 85%, and in examples satisfying 0.45≤X≤0.87, it was more than 90%.

All publications, patents, and patent applications cited in this specification are hereby incorporated by reference.

100: positive electrode
110: Positive electrode mixture layer
120: positive electrode current collector
130: positive electrode tab
200: negative electrode
210: Negative mixture layer
220: negative electrode current collector
230: negative electrode tab
300: insulating layer
400: electrode body
500: exterior body
1000: Lithium ion secondary battery

Claims (8)

A solvated ionic liquid having at least one of sulfolane and its derivatives and an electrolyte salt, a low viscosity organic solvent, and a negative interface stabilizer,
The low viscosity organic solvent is propylene carbonate, butylene carbonate, ethylene carbonate, trimethyl phosphate, triethyl phosphate, tris(2,2,2-trifluoroethyl) phosphite, γ-butyrolactone, or It is dimethyl methylphosphonate,
The negative electrode interface stabilizer is vinylene carbonate or fluoroethylene carbonate,
The equilibrium vapor pressure of the low-viscosity organic solvent at room temperature is 1 Pa or more,
Let X be the ratio of the number of moles of the solvated ionic liquid to the total number of moles of the solvated ionic liquid and the low-viscosity organic solvent,
When the ratio of the weight of the negative electrode interface stabilizer to the total weight of the solvated ionic liquid and the low-viscosity organic solvent is Y (%),
0.35≤X<1
Y≥3
Y≤142.86X-11.429
A non-aqueous electrolyte that satisfies. delete According to paragraph 1,
0.39≤X≤0.93
Phosphorus, non-aqueous electrolyte. According to paragraph 1,
0.45≤X≤0.87
Phosphorus, non-aqueous electrolyte. According to paragraph 1,
A non-aqueous electrolyte solution in which the donor number of the low-viscosity organic solvent is 12 or more. A semi-solid electrolyte layer comprising the non-aqueous electrolyte solution according to any one of claims 1 and 3 to 5, supporting particles, and a semi-solid electrolyte binder. A secondary battery sheet comprising at least one of a positive electrode and a negative electrode and the semi-solid electrolyte layer according to claim 6 laminated. Positive polarity,
negative polarity,
The semi-solid electrolyte layer according to claim 6, disposed between the positive electrode and the negative electrode.
A secondary battery comprising:

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